Castle Rock in Pine Canyon is closed for peregrine falcon nesting season, from February 1 through July 31st, 2015. All other Mount Diablo area crags are open to climbing. The news release is linked here.

This information is a public crowdsourcing effort between the Access Fund,
and Mountain Project.You should confirm closures, restrictions, and/or related dates.

Description

The Rock of Ages is found just behind the Pagoda. It has a large distinctive cave half way up the wall. The rock can range form crumbly and loose to solid and clean. The base of this wall is a great place to hang out when the temps soar. You can always find shade and a nice cool breeze comes up from the bottom of the canyon. This rock sees the most traffic in the canyon, but you'll still be lucky to see anyone.

Getting There

From Stage Road (the main fire trail) The Rock of Ages shares its approach with Pulpit and Pagoda Rock. On the left of the trail is a wooden post for Nature Walk 8. Past that on the right is a post for Nature Walk 11, then a bench, then Nature Walk 10. Shortly after that, on the left, is the straight, narrow, well-worn dirt trail you want (goes uphill and to the right). Immediately after the trail entrance is a small dried creek. If you hit the post for Nature Walk 9 you've gone too far. If you hit the green gate you've gone even farther.

After a short hike up the trail and over some rocks you'll see Pulpit on the left. It's the first area and it's hard to miss with its bolted route right next to the approach. Shortly up past Pulpit is Pagoda Rock, and shortly up past that is The Rock of Ages. Getting from Pagoda to Rock of Ages requires scrambling over some big rocks.

Starts 40 ft to the right of the Cave Route and climbs up past five bolts into a cave, belay here on three bolts. Exit the cave to the right and continue up and slightly to the left past another cave and bolt. Now move out right and follow the natural line. Don't worry if you don't see the bolts. You're probably still on route, they'll show up eventually. There's a large loose block about half way up you have to crawl over to avoid harder moves. It would take some prying to pull it off, but care...[more]Browse More Classics in CA

A little bit of access info for finding Rock of Ages. We went on quite the scramble to eventually find the area following the somewhat vague map in the Bay Area rock guide.

For the trail that leads straight up to Rock of ages (ie the cave route, etc):

Follow the fire road from the parking lot as the guide book says. Keep hiking until you hit the #10 trail marker post. Keep hiking another 100-200 feet and take the well travelled single track trail that climbs off and to the left of the fire road, essentially working its way up the creek and becoming a drainage.

As stated for the area, it is a tough approach, very steep and loose, but if you can manage to start up the correct drainage and actually end up at the base of the climb you are searching for you will save a few hours of your day scrambling up high on the hill!

And I will second the graffiti and trash comment. Truly disgusting, but I would put my money on the fact that it is 99% from non-climbers using the area as an escape from the city to tag up the rock. I will be bringing a full size garbage bag next time I head up, and would encourage the same for others.... It was frustrating being up there climbing with no way to pack anything out.

I'm willing to bet big money that the trash and graffiti is 100% not from climbers. The place has had some trash and graffiti over the years. Especially lower down toward the bottom of the canyon. But the volume of trash and spray paint has increased ten fold over the past two or so years.

The description in the Bay Area guide (assuming you're referring to the new Thornburg guide) is no more vague than yours.

Spot the Rock of Ages and Pagoda from the main trail. Find the dry creek/gully that goes up just to it's climbers right side. BOOM!!! You're there...

Jskierpx commented that the approach trail is past trail marker #10 but it's really just after #8: From the main fire trail The Rock of Ages shares its approach with Pulpit and Pagoda Rock. On the left of the trail is a wooden post for trail marker #8. Soon after that, on the left, is a straight, narrow, well-worn dirt trail that goes uphill and to the right. Immediately after the trail entrance, on the left, is a small dried creek. If you hit trail marker #9 you've gone too far. If you hit the green gate you've gone even farther. After a short hike up the trail and over some rocks you'll see Pulpit on the left. It's the first area and it's hard to miss with its bolted route right next to the approach. Shortly up past Pulpit is Pagoda Rock, and shortly up past that is The Rock of Ages.